Could be a capacitor in the electric box on the unit (easy replacement once diagnosed) , or could be a bad blower motor (unit must be pulled out). And there are two fans/ blowers ... inside blower & outside blower.

The whole HVAC unit has to come out of RV just to change a fan motor??

The top of the unit must be removed to get access to blowers & compressors, so the unit must be pulled out. Not a big deal for someone who knows what they are doing, but most service places charge $300 or more just for the labor.

There's some diagnostic LEDs on the control board that might provide a clue to the problem. Remove a few screws on the basement panel, swing it up (it should be hinged at the top) and prop it open. Remove the steel cover plate on the HVAC unit. Grab your service manual from RVP.